Chemical bond approach to the electronic structure of amorphous semiconductors

The electronic structure of amorphous semiconductors with various compositions is described by the assembly of bonding, antibonding and lone-pair orbitals. Energy levels for these orbitals are calculated by extended Hückel theory. Broadening of the levels due to the interaction among chemical bonds and/or lone-pairs is determined empirically. The present calculation is free from detailed atomic structures. The changes of densities of valence states, average energy gaps and optical gaps with composition are calculated for various amorphous semiconductors. The results agree rather well with the observed ones.